The present invention is related generally to latch and lock mechanisms for doors, and more particularly, to latch and lock mechanisms for aircraft cargo door assemblies.
Certain cargo transport airplanes include a central bay cargo door assembly in the underside of the fuselage. The doorway opens downwardly and rearwardly from the rear of the airplane where the underside of the fuselage slopes upwardly to the tail section, such that cargo and vehicles may be loaded into the fuselage from directly behind the airplane. The particular type of door assembly to which the present invention is directed is formed in two parts: a cargo ramp hinged to the fuselage at the forward, or lower, edge of the doorway; and a cargo door hinged to the fuselage at the upper, rear edge of the doorway. With the door assembly closed, the cargo ramp and the cargo door meet in the middle of the doorway in coplanar alignment so as to form a two-part, pressure-tight closure member. To open the door assembly for loading and unloading cargo, the cargo ramp is swung downwardly to extend to the ground, and the cargo door is swung upwardly into the overhead space in the rear of the fuselage. The cargo door is swung upwardly in such a manner to provide adequate vertical clearance for vehicles entering and exiting the airplane on the cargo ramp. Since the cargo door swings inwardly, it is ordinarily a plug-type door, whereas the outwardly swinging cargo ramp is necessarily a nonplug-type closure member.
Failure of an aircraft door latch mechanism during flight, or inadvertent unlatching during flight due to human error, can result in the cabin pressurization and the outside airstream blowing the door open with sufficient force to damage the door and impair the stability of the airplane. Several catastrophic accidents have in fact been caused in recent years by the unexpected and violent opening of aircraft door assemblies during flight. These accidents have resulted from various causes, including mechanical failures of the door latch mechanisms as well as human errors, such as inadvertently leaving cargo doors in closed but unlatched positions prior to takeoff. These failures have prompted a search for a safe, simple, and reliable latch and lock mechanism for the above-described type of cargo door assembly.
Accordingly, it is an object and purpose of the present invention to provide a safe, simple and reliable latch and lock mechanism in an airplane door assembly having an outwardly opening closure member, such as a loading ramp, and an inwardly opening door member.
It is also an object to provide such a door assembly having a latch and lock mechanism that includes a mechanical interlock between the cargo door and cargo ramp, such that the cargo door cannot be inadvertently closed when the cargo ramp is in a closed but unlatched position. It is also an object to provide such a latch and lock mechanism wherein the mechanical interlock between the cargo door and cargo ramp is independent of the latch mechanism for the cargo ramp.
It is another object to provide a latch and lock mechanism that positively prevents the cargo ramp from being unlatched until the fuselage cabin has been depressurized and the cargo door has been unlatched and at least partially opened.